Source : Webster's Revised Unabridged Dictionary (1913)

Momentaneous \Mo`men*ta"ne*ous\, Momentany \Mo"men*ta*ny\, a.
   [L. momentaneus: cf. F. momentan['e].]
   Momentary. [Obs.] --Hooker. ``Momentany as a sound.'' --Shak.

Source : WordNet®

momentaneous
     adj : lasting for a markedly brief time; "a fleeting glance";
           "fugitive hours"; "rapid momentaneous association of
           things that meet and pass"; "a momentary glimpse" [syn:
            {fleeting}, {fugitive}, {momentary}]